[tor-commits] [torspec/main] Clarify handling of dubious RELAY_END cell formats.

[nickm at torproject.org]

commit a681521b9d04135d2cff5d20b82927162c6626cc
Author: Nick Mathewson <nickm at torproject.org>
Date:   Mon Aug 16 11:25:08 2021 -0400

    Clarify handling of dubious RELAY_END cell formats.
---
 tor-spec.txt | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/tor-spec.txt b/tor-spec.txt
index a3a0ffd..4d9513e 100644
--- a/tor-spec.txt
+++ b/tor-spec.txt
@@ -1817,25 +1817,31 @@ see tor-design.pdf.
       14 -- REASON_NOTDIRECTORY   (Client sent RELAY_BEGIN_DIR to a
                                    non-directory relay.)
 
+   [*] Older versions of Tor also send this reason when connections are
+       reset.
+
+   OPs and ORs MUST accept reasons not on the above list, since future
+   versions of Tor may provide more fine-grained reasons.
 
-   For most reasons, the format is:
+   For most reasons, the format of RELAY_END is:
 
       Reason                      [1 byte]
 
-   For REASON_EXITPOLICY, the format is:
+   For REASON_EXITPOLICY, the format of RELAY_END is:
 
       Reason                      [1 byte]
       IPv4 or IPv6 address        [4 bytes or 16 bytes]
       TTL                         [4 bytes]
 
-   OPs and ORs MUST accept reasons not on the above list, since future
-   versions of Tor may provide more fine-grained reasons.
+   (If the TTL is absent, it should be treated as if it were 0xffffffff.
+   If the address is absent or is the wrong length, the RELAY_END message
+   should be processed anyway.)
 
    Tors SHOULD NOT send any reason except REASON_MISC for a stream that they
    have originated.
 
-   [*] Older versions of Tor also send this reason when connections are
-       reset.
+   Implementations SHOULD accept empty RELAY_END messages, and treat them
+   as if they specified REASON_MISC.
 
    Upon receiving a RELAY_END cell, the recipient may be sure that no further
    cells will arrive on that stream, and can treat such cells as a protocol